The present invention relates generally to multi-level converters and in particular to control methods for controlling the operation of the multi-level converter.
Converters are employed in a variety of applications to convert direct current (DC) power to alternating current (AC) power and vice versa. A converter for DC-to-AC conversion is referred to as an inverter, while an AC-to-DC converter is referred to as a rectifier. Employing active components, such as transistors, allows for regulation of the voltages generated by the converter. Multi-level converters, for example, may be employed to generate two-level outputs in rectifier operations such that a positive DC output and a negative DC output are generated.
A Vienna-type rectifier is an example of a multi-level rectifier that provides a two-level DC bus with unidirectional power flow and power factor correction. In particular, the Vienna-type rectifier provides a reduced switch count realization of a three-phase, three-level AC-DC converter. Active components within the Vienna-type rectifier are selectively controlled to generate the desired DC voltage on both the positive and negative DC bus (i.e., the two-level DC bus).
Space vector modulation is a control scheme commonly used in conjunction with converters and has been applied to Vienna-type rectifiers. A space vector plot defines each combination of switch states associated with the Vienna-type rectifier. Each switch state defines a configuration of the active components or switches within the multi-level converter. Control of the multi-level converter requires the selective traversal of adjacent switch states in the space vector plot. Space vector modulation may be employed with a variety of multi-level converters, including Vienna-type rectifiers and Rockford-type rectifiers.